The objective of this project is to explain at the molecular level the regulation of gene transcription during the differentiation of the Gram-positive bacterium Bacillus subtilis into a spore. A segment of B. subtilis DNA has been cloned that contains two genes whose transcription is under sporulation control. This cloned chromosomal segment maps in the PurA-cysA region of the chromosome and at least one of the sporulation controlled genes corresponds to a genetically-defined sporulation locus. Two modified forms of B. subtilis RNA polymerase have been isolated that direct specific transcription of the cloned sporulation genes. These modified RN polymerases lack the usual B. subtilis sigma factor (sigma 55) but contain instead novel sigma-like factors of 37,000 (sigma 37) or 29,000 (sigma 29) daltons. The possibility that sigma 37 and sigma 29 are regulatory proteins that control developmental gene expression is under investigation.